1. Field of the Invention
The present invention relates to an aluminum alloy clad material for heat exchangers exhibiting excellent erosion-corrosion resistance. The aluminum alloy clad material comprises an aluminum alloy clad sheet for heat exchangers exhibiting excellent erosion-corrosion resistance which comprises the aluminum alloy clad material and is suitably used for forming a tube material or header plate material in the manufacture of aluminum heat exchangers such as a radiator and heater by brazing in an inert atmosphere using a fluoride-type flux or vacuum brazing, and an aluminum alloy clad pipe comprising the aluminum alloy clad material which is used for tubes for circulating a working fluid in the aluminum heat exchanger such as a radiator and heater and for a pipe connected to heat exchangers, and is mechanically assembled into a fin of a heat exchanger using a pipe expansion method and the like.
2. Description of Background Art
As a tube material or header plate material for an automotive radiator, heater, and the like, a two-layered clad sheet comprising a core material of an Al--Mn alloy such as a 3003 alloy clad with a brazing material of Al--Si alloys or a sacrificial anode material of an Al--Zn alloy or an Al--Zn--Mg alloy on the outer side has been used. In some cases, a three-layered clad sheet comprising a core material of an Al--Mn alloy such as a 3003 alloy clad with a brazing material of an Al--Si alloy on one side and a sacrificial anode material of an Al--Zn alloy or Al--Zn--Mg alloy clad on the other side has been used.
In the manufacture of a radiator or heater, tubes are formed by curving the clad sheet with the brazing material of an Al--Si alloy or the core material being on the outer side and welding or brazing the clad material. The tube is joined to a fin or header plate via the brazing material of the tube material or a brazing material clad on the fin by inert atmosphere brazing using a fluoride-type flux or vacuum brazing. The sacrificial anode material on the inner surface of the tube material exhibits a sacrificial anode effect by being in contact with a working fluid during use to prevent occurrence of pitting or crevice corrosion of the core material. The fin material prevents the core material from pitting by exerting a sacrificial anode effect on the core material.
A clad pipe with a two-layered structure in which an Al--Zn alloy as an inner layer (sacrificial anode material layer) is clad on an Al--Mn alloy such as a 3003 alloy as an outer layer (core material layer), or a clad pipe with a three-layered structure in which an outermost layer (sacrificial anode layer) of an Al--Zn alloy is further clad on the outside the piping material has been also used. In this case, the inner layer of the clad pipe exhibits a sacrificial anode effect on the core material layer of an Al--Mn alloy by being in contact with the working fluid to prevent the core material layer from pitting. In the case of the clad pipe with a three-layered structure, the outermost layer prevents occurrence of pitting or crevice corrosion of the core material layer by exerting a sacrificial anode effect on the core material layer made of an Al--Mn alloy.
As a working fluid for heat exchangers and pipes, a neutral or weak alkaline solution prepared by diluting a commercially available antifreeze fluid containing ethylene glycol as an essential component with water to a concentration of 50 vol % is commonly used. Some working fluids may cause erosion-corrosion in the aluminum alloy clad material (clad sheet and clad pipe) constituting a tube, and the corrosion perforates the core material or core material layer to impair heat exchanging properties.
Some materials for aluminum heat exchangers such as a radiator or heater exhibiting improved pitting resistance have been proposed. One of such materials is an aluminum alloy clad material made of a core material of an Al--Mn alloy containing 0.2-1.5% of Mn, 1.0% or less of Si, and one or more of 0.5% or less of Cu, 0.3% or less of Cr, and 0.2% or less of Zn as required, a brazing material of an Al--Si alloy clad on one side of the core material, and a sacrificial anode material of an aluminum alloy containing 2% or less of Zn clad on the other side of the core material (Japanese Patent Application Laid-open No. 94993/1991). The other example is an aluminum alloy clad material made of a core material of an aluminum alloy containing 0.3-2% of Mg, 0.3-1.5% of Si, 0.02-0.8% of Cu, and one or more of 0.05-0.3% of Mn, 0.02-0.5% of Cr, and 0.02-0.2% of Zr as required, a conventional brazing material of an Al--Si alloy clad on one side of the core material, and a sacrificial anode material of an aluminum alloy containing 0.2-3% of Zn, 0.005-0.05% of In, and 0.05-0.2% of Sn clad on the other side of the core material (Japanese Patent Application Laid-open No. 132284/1996).
These aluminum alloy clad materials exhibit an excellent sacrificial anode effect as a tube material for a radiator or heater, if the working fluid is neutral or weakly acidic and includes a Cl ion and has a relatively low temperature. However, if the working fluid is weakly alkaline and flows inside a heat exchanger at a high velocity, these materials exhibit insufficient corrosion resistance, thereby causing erosion-corrosion due to the insufficient anti-corrosion effect.